1. Field of the Invention
The present invention relates to a seal element suitable for use in an air conditioner system to provide a seal between opposed ducts of the air conditioner system. There is also a method for making such seal element.
2. Prior Art
A number of elastic seal elements made in various shapes are known and used for providing a seal by being squeezed between opposed surfaces of two adjacent ducts of an air conditioner system installed in an automobile, for example.
Once such known seal element is disclosed in Japanese Utility Model Laid-open Publication No. 56-135564. The disclosed seal element has a square cross-sectional shape, and because of this cross-sectional-sectional shape, it performs satisfactorily only when installed correctly. More specifically, the square seal element fits flatwise against opposed surfaces of two adjacent ducts when diametrically squeezed on installation, however, it is likely to tilt when subjected to forces applied in a direction parallel to a seal plane during installation.
When installed in such tilted condition, the square seal element is intensely squeezed at its diagonal corner edges whereas opposite surfaces of the same element come out of contact with the opposed ducts surfaces. As a result, only a small sealing area is provided between the tilted seal element and each duct surface, which would cause leakage of condensed moisture under osmotic pressure.
Another seal element shown in the above-mentioned Japanese document has outwardly swelled sealing surface engageable with opposed surfaces of two adjacent ducts. This seal element is elastically deformable to engage with the duct surfaces substantially over the entire regions of the respective sealing surfaces even when subjected to forces applied parallel to a seal plane during installation. Contrary to the largeness of the sealing area, the sealing element has a small amount of compression which gives a small sealing pressure to the duct surfaces. With this arrangement, moisture leak would take place at the joint.
Japanese Utility Model Laid-open Publication No. 48-94337 discloses a seal element formed from a foamed material, such as foamed rubber or foamed plastics, into a semi-circular or substantially D-shaped cross section. The disclosed seal element also has the same drawback as the foregoing element.
In summary, the prior seal elements are disadvantageous in that a fluid-tight seal is difficult to achieve due to imbalance between the sealing area and the sealing pressure depending on the compressibility of the individual sealing elements.
It is customary practice to make a seal element of a foamed material either by (a) vulcanizing unvulcanized rubber foam in a heated mold, (b) extruding a foamed material form a shaping die, (c) molding a molten compound such as polyurethane form, or (d) compressing a foam sheet between a pair of molds jointly defining grooves of an accurate cross section. Neither of the foregoing methods has been found satisfactory.
Vulcanizing requires a relatively long processing time and is likely to produce seal elements whose properties vary with the degree of vulcanization particularly when a high extent of forming is intended. Extrusion is disadvantageous in that foamed seal elements of uniform quality are difficult to obtain particularly when extruding an open-cell foamed material at a high rate of extrusion. Compound molding requires a number of molds for moss-production and hence is expensive, is incapable of continuous operation and less efficient. Another drawback associated with compound molding is in that the molten material, as it is cured in the mold, is likely to create pinholes or to cause local pealing-off of a skin due to charge in the mold temperature.
Compression forming is achieved in the manners shown in FIGS. 8(a) and 8(b) of the accompanying drawings. As shown in FIG. 8(a), a foam sheet 80 is placed between an upper shaping die 81 and a lower planar die 82, the shaping die 81 and a lower planar die 82, the shaping die 81 including a plurality of downwardly open, parallel spaced grooves 83 of a U-shaped cross-section. Then, the upper shaping die 81 and the lower die 82 are moved toward each other to compress the foam sheet 80 therebetween, thereby producing a blank seal element 84 comprising a plurality of substantially semicylindrical bodies 85 joined together by narrow webs 86. Finally, the blank seal element 84 is cut along the webs 86 into the individual semicylindrical bodies 85 each of which constitutes a foamed seal element. The seal element 85 includes an upper accurate surface 87 engageable with are duct, and flat lower surface 88 engageable with the other duct, the seal element 85 having a thickness h. The upper accurate surface 87 is stretched greater than the lower flat surface 88 so that the surface 87 has a larger extent than the surface 88. The seal element 85 thus obtained has a limited thickness even when formed with upper shaping die having grooves of a larger depth H. The highly stretched and compressed upper region is dense and hence has a low elasticity, so it is difficult to use such seal element 85 at a corner joint. Furthermore, the seal element 85 is relatively thin and hence is not suitable for use in an automobile air conditioner system wherein a space between opposed surfaces of two adjacent ducts is relatively large due to accumulated tolerances caused form working and assembling of components of the air conditioner system.